Evaluation of streaming electrification considering circulation of charged oil

Streaming electrification occurs when the insulated oil passes through the ducts of insulating paper in a transformer. While the generated electrostatic charge circulates, a high voltage can build up at some parts. In the case that an extremely low conductivity oil is used, the voltage increases because of the large relaxation time. If the relaxation time is comparable to the circulation time of oil, the electrostatic charge accumulates increasing the voltage further. This paper is concerned with the effect of the macroscopic electrostatic charge accumulation. The charge relaxation process is observed experimentally. Based on the relaxation relation, the charge density and voltage rise are evaluated for actual transformers